1. Field of the Invention
The present invention relates generally to circuit breakers and, more particularly, to a load conductor of a circuit breaker. Specifically, the invention relates to a load conductor employing a load terminal and a conductive tang connected therewith, the tang enhancing the electrical conductivity of the load terminal.
2. Description of the Related Art
Numerous types of circuit breakers are known and understood in the relevant art. Among the purposes for which circuit breakers are provided is to interrupt electrical current on command or under certain defined circumstances. Generally stated, most circuit breakers include a line conductor connected with a power source and a load conductor connected with an electrical load, and further include a current interruption system interposed between the line conductor and the load conductor to interrupt current as needed. The current interruption system typically includes an operating mechanism that separates a set of separable electrical contacts to interrupt current from flowing therethrough, and further includes a trip unit operatively connected with the operating mechanism. The trip unit triggers the operating mechanism to separate the electrical contacts during the specified overcurrent, under-voltage, or other condition. In multi-phase circuit breakers, the operating mechanism typically includes a crossbar that simultaneously separates several sets of separable contacts to simultaneously interrupt current through all of the phases of the circuit breaker.
The trip unit typically includes one or more types of tripping mechanisms that are each able to trigger the operating mechanism to interrupt the current under specified conditions. One type of trip mechanism is a thermal trip that includes a bimetallic strip employing at least two layers of metal having different coefficients of thermal conductivity, with the bimetallic strip deflecting and triggering the operating mechanism under certain overcurrent conditions that last for a certain duration of time. Such bimetallic strips rely upon heat generated due to the electrical resistance of the bimetallic strip and of other components of the circuit breaker to the current flowing through the circuit breaker during operation thereof. Other types of tripping mechanisms include magnetic trip mechanisms, blow-open trip mechanisms, and manual trip mechanisms, as well as other trip mechanisms.
Further regarding thermal trip mechanisms, depending upon the configuration of the bimetallic strip and of the circuit breaker as a whole, it typically is desirable to avoid contacting the bimetallic strip with other conductors that are at relatively low temperatures in order to avoid the heat generated within the bimetallic strip from being shunted away to the relatively lower temperature component. In this regard, it has thus been known to manufacture out of stainless steel or other such material a load terminal to which the bimetallic strip is mounted. The stainless steel generates a given amount of heat during operation of the circuit breaker, thus maintaining the load terminal at a relatively high temperature and likewise resisting the shunting of heat from within the bimetallic strip to the load terminal.
Due to size limitations of some circuit breakers, it may also be desirable to augment the heat generated by electrical resistance within the metallic strip with heat that is generated by electrical resistance within other components of the circuit breaker that are in thermally conductive engagement with the bimetallic strip, such as the load terminal. In such applications the load terminal is specifically configured to conduct heat due to electrical resistance therein to the bimetallic strip.
The use of such relatively resistive load terminals has not, however, been without limitation. Depending upon the configuration of the circuit breaker, many load terminals are formed with a right angle bend in order to permit the electrical load to be connected with the load terminal. The bend in such a load terminal often has a tendency to become unduly hot during operation of the circuit breaker.
It has also been observed that clamped joints (such as the clamped joint between the load terminal and the load) become unduly hot during operation of the circuit breaker due to imperfections in the contacting surfaces of the components being clamped and for other reasons. During high fault conditions, therefore, portions of the load terminal that are adjacent such clamped joints can become fused to the load or may result in loss of the material of the load terminal or other undesirable circumstances. Nevertheless, it is still desired to maintain the load terminal at a certain elevated temperature during operation of the circuit breaker to avoid interference with the function of the bimetallic strip by failing to conduct heat thereto or by shunting heat therefrom.
It is thus desired to provide an improved load conductor for a circuit breaker that generates a desirable amount of heat due to electrical resistance during operation of the circuit breaker, yet that is generally not susceptible of fusing or other failure during high fault conditions of operation.
In view of the foregoing, a load conductor for use with a circuit breaker includes a load terminal and a conductive tang electrically engaged with one another. The load terminal is manufactured out of a first material having a first electrical conductivity, and the tang is manufactured out of a second material having a second electrical conductivity. The first electrical conductivity of the first material is such that the load terminal remains at a desirably high temperature during operation of the circuit breaker to avoid interference with the function of a bimetallic strip mounted on the load terminal. The tang extends across a bend formed in the load terminal to avoid the bend from becoming undesirably hot during operation of the circuit breaker. The tang also provides additional conductive cross-section and a higher conductivity surface to reduce the temperature of the load terminal in the vicinity of the clamped joint between the load terminal and the load.
An objective of the present invention is to provide a load conductor for a circuit breaker in which a load terminal of the load conductor maintains a desirably high temperature during operation of the circuit breaker.
Another objective of the present invention is to provide a load conductor for a circuit breaker in which a bend formed in a load terminal of the load conductor does not become undesirably hot during operation of the circuit breaker.
Another objective of the present invention is to provide a load conductor for a circuit breaker in which the load conductor is advantageously configured to avoid interference with the operation of a bimetallic strip mounted on the load conductor.
Another objective of the present invention is to provide a load conductor for a circuit breaker in which the load conductor is advantageously configured to reduce the temperatures of the load conductor at the clamped joint between the load conductor and the load.
Another objective of the present invention is to provide a circuit breaker having a load conductor that does not interfere with the function of a thermal trip mechanism of the circuit breaker, with the load conductor being substantially immune to fusing with the load during high fault conditions.
An aspect of the present invention is thus to provide a tang for conductive engagement with a load terminal of a circuit breaker, in which the load terminal is made out of a first material having a first electrical conductivity, and in which the load terminal includes an extension portion and a connection portion and is formed with a bend interposed between the extension and connection portions, with the circuit breaker including a thermal trip mechanism connected with the load terminal, and the load terminal being structured to conduct heat due to electrical resistance to the thermal trip mechanism during operation of the circuit breaker, in which the general nature of the tang can be stated as including a first member and a second member connected with one another. The first and second members are each substantially planar and are non-parallel with one another, with the first and second members being formed of a second material having a second electrical conductivity. The first member is structured to be electrically conductively engaged with the extension portion of the load terminal, and the second member is structured to be electrically conductively engaged with the connection portion of the load terminal.
The second electrical conductivity may be greater than the first electrical conductivity.
The extension and connection portions of the load terminal may be oriented at a given angle with respect to one another, with the first and second members being oriented with respect to one another at the given angle.
Another aspect of the present invention is to provide a load conductor for use with a circuit breaker, in which the circuit breaker includes a thermal trip mechanism that is structured to be connected with the load conductor, with the load conductor being structured to conduct heat due to electrical resistance to the thermal trip mechanism during operation of the circuit breaker, in which the general nature of the load conductor can be stated as including a load terminal and a tang. The load terminal includes an extension portion and a connection portion and is formed with a bend interposed between the extension and connection portions. The tang includes a first member and a second member connected with one another. The first member is electrically conductively engaged with the extension portion, and the second member is electrically conductively engaged with the connection portion. The tang extends less than fully along the extension portion of the load terminal.
Still another aspect of the present invention is to provide a circuit breaker, the general nature of which can be stated as including a line conductor, a load conductor, and a thermal trip mechanism connected with the load conductor, the load conductor including a load terminal and a tang. The load terminal includes an extension portion and a connection portion and is formed with a bend interposed between the extension and connection portions. The tang includes a first member and a second member connected with one another, with the first member being electrically conductively engaged with the extension portion, and with the second member being electrically conductively engaged with the connection portion. The load terminal is structured to conduct heat due to electrical resistance to the thermal trip mechanism during operation of the circuit breaker.